Fast Pulse Generator

ABSTRACT

A pulse generator including a pulsed switch ( 12 ), for example a diode, connected between an input source ( 14 ), such as an oscillator, and a frequency multiplier ( 16 ).

The present invention relates to a fast pulse generator, and inparticular a fast radio frequency pulse generator having an output inthe frequency range of tens of kilohertz to 100s of gigahertz.

FIG. 1 shows a conventional radio frequency switch pulse generator. Thishas an oscillator that is connected to a pulsed switch, thereby toprovide a fast, pulsed output. In practice, the switch is typically adiode. A disadvantage of this arrangement is that the switch parametersdetermine the output pulse width. A further limitation is that when adiode is used, pulse rise times are limited by the intrinsic bandwidthof the switch pulse input, which in turn limits the output pulse risetime. In addition, the switch has an insertion loss, which reduces theoutput power. Also, the output power is restricted by the power handlingcapability of the switch. Any attempt to overcome the losses using anamplifier, places restrictions on the amplifier bandwidth, and asfrequency increases these restrictions become more difficult to satisfy.

An object of the present invention is to provide an improved fast pulsegenerator.

According to one aspect of the present invention, there is provided apulse generator including a pulsed switch connected between an acsource, such as an oscillator, and a non-linear frequency multiplier.

Because the frequency multiplier is a non-linear device that onlyconducts above a threshold and saturates very quickly, an effectivesharpening of the pulse edges is provided, which allows for thegeneration of shorter, and so faster, output pulses.

The pulsed switch may be a semiconductor diode. The pulsed switch may bea mixer means. The switch may be operable to produce bi-phase pulses.The switch may be operable to produce multi-phasic pulses.

A plurality of frequency multipliers may be provided. In this case, thepulsed switch may be provided between adjacent multipliers.

The generator may include at least one amplifier. The amplifier may beconnected between the pulsed switch and the frequency multiplier. Wherea plurality of frequency multipliers is provided, the amplifier may beconnected between two of these multipliers. The amplifier may beconnected to an output of the frequency multiplier.

The pulse generator may be configured to provide a pulsed output havinga frequency in the range of tens of kilohertz to 100s of gigahertz.

The pulse generator may be fabricated on a single chip, making it idealfor inclusion in integrated circuits. Alternatively, the generator couldbe constructed from separate components.

Various aspects of the invention will now be described by way of exampleonly and with reference to the accompanying drawings, of which:

FIG. 2 is block diagram of a pulse generator;

FIG. 3 is modified version of the pulse generator of FIG. 2;

FIG. 4 is another modified version of the generator of FIG. 2;

FIG. 5 is yet another modified version of the generator of FIG. 2, and

FIG. 6 is still another modified version of the generator of FIG. 2.

FIG. 2 shows a pulse generator 10 including a pulsed switch 12 connectedbetween an oscillator 14 and a frequency multiplier 16. Any suitableoscillator 14 could be used, provided it is able to drive the frequencymultiplier non-linearly 16. The multiplier 16 may include one or morenon-linear devices, for example one or more varactor diodes, FETs,bipolar or other types of diode. Although FIG. 2 shows only a singlefrequency multiplier 16, there may be a plurality of these, with thepulsed switch 12 connected between adjacent multipliers, as shown inFIG. 3. The pulsed switch 12 may be a semiconductor device or a mixermeans, for example, a diode or a four-quadrant multiplier or doublebalanced mixer or any other relatively fast switch. In any case, theswitch 12 may be operable to produce bi-phase pulses. Alternatively, theswitch 12 may be operable to produce multi-phasic pulses.

Because the multiplier 16 of FIGS. 2 and 3 is a nonlinear device thatonly conducts above a threshold and saturates very quickly, an effectivesharpening of the pulse edges is observed. In practice, this means thatthe pulses are shorter and so faster.

Various device configurations have been tested. In one example, theoscillator 14 was a YIG (Yttrium Iron Garnet) oscillator tunable from6.8 to 8.8 GHz with a power output of +15 dBm, followed by a varactordiode multiplier chain. The gating switch pulse width was 600 ps atabout 100 MHz. This provided output pulses having a width of 260 ps at94 GHz. In another example, the oscillator used was a dielectricresonator oscillator, which provided a fixed frequency of 7.833 GHz,followed by a varactor diode multiplier chain. In this case, the gatingswitch pulse width was 1 ns at about 100 MHz and the output pulses had awidth of 650 ps at 94 GHz. These examples are by no means exclusive, butinstead are provided for the purposes of illustrating the benefits ofthe invention. The type of oscillator and required output power aredependant only upon system requirements.

The pulse generator in which the invention is embodied can be used formany applications, particularly radar applications. For example, theinvention could be of particular use in radar based collision avoidancesystems. Because of the very high speeds achievable using the generator,the accuracy and resolution of such systems would be greatly improved.

A skilled person will appreciate that variations of the disclosedarrangements are possible without departing from the invention. Forexample, because processing by the frequency multiplier will reduced thepulse signal amplitude, at least one amplifier 18 may be provided forrecovering that pulse amplitude. This may be provided between the pulsedswitch 12 and the frequency multiplier 16, as shown in FIG. 4. Where aplurality of frequency multipliers 16 is provided, the amplifier 18 mayprovided between two of these multipliers 16, as shown in FIG. 5.Alternatively or additionally, the amplifier 18 may be connected to anoutput of the frequency multiplier 16, as shown in FIG. 6. Accordinglythe above description of the specific embodiment is made by way ofexample only and not for the purposes of limitation. It will be clear tothe skilled person that minor modifications may be made withoutsignificant changes to the operation described.

1. A pulse generator including a pulsed switch connected between an acinput source and a non-linear frequency multiplier.
 2. A pulse generatoras claimed in claim 1 wherein the pulsed switch is a semiconductordiode.
 3. A pulse generator as claimed in claim 1 wherein the pulsedswitch is a mixer.
 4. A pulse generator as claimed in claim 1 wherein aplurality of frequency multipliers is provided and the pulsed switch isprovide between adjacent such multipliers.
 5. A pulse generator asclaimed in claim 1 including at least one amplifier.
 6. A pulsegenerator as claimed in claim 5 wherein an amplifier is between thepulsed switch and the frequency multiplier.
 7. A pulse generator asclaimed in claim 5 wherein a plurality of frequency multipliers isprovided and an amplifier is provided between two of these multipliers.8. A pulse generator as claimed in claim 5 wherein an amplifier isconnected to an output of the frequency multiplier.
 9. A pulse generatoras claimed in claim 1 wherein the pulsed switch is operable to producebi-phase pulses.
 10. A pulse generator as claimed in claim 1 wherein thepulsed switch is operable to produce multi-phasic pulses.
 11. A pulsegenerator as claimed in claim 1 wherein the ac input source is anoscillator.